Coke oven with gas recirculation means



Dec. 25, 1951 w. NASH COKE OVEN WITH GAS RECIRCULATION MEANS 3Sheets-Sheet l 'Filed Feb. 19, 1949 Inventor CYRIL zaza/7 /Vvsf/Attorney Dec." 25, 1951 Filed Feb. 19. 1949.

A c. w. NASH COKE OVEN WITH GAS RECIRCULATION MEANS 3 Sheets-Sheet 2 IAttorney ".Dec. z5, 1951 Filed Feb. 19, 1949 3 Sheets-Sheet 5 InventorCreu.- @Lawn/W95# Patented Dec. 25, 1951 CQKE OVEN WITH GASRECIBCULATION MEANS Cyril William Nash, London, England, assigner to TheWoodall-Duckham Vertical Retort and Oven Construction Company (1920)Limited, London, England, a British company Application February 19,1949, Serial No. 77,367 In Great Britain February 24, 1948 6 claims. i

This invention concerns improvements in or relating to coke ovens andhas particular reference to batteries of coke ovens of the typedescribed in the speciilcation of United States Patent numbered1,752,363, in which horizontal ovens are arranged side by side withheating nues on either side of each oven, and in which each of theseovens or each of a group of such ovens is connected with commoncollecting mains for recovering the gas distilled from the coal beingcarbonized, the said collecting mains being arranged along both sides ofthe battery (usually at the crown of the latter) and being connectedtogether by an arched oftake main or cross-duct connected-usuallycentrally-through a T-joint to a suction main through which thegenerated gases are removed. l

The ovens are charged to a predetermined level with coal that is to becarbonized, the coal is levelled, carbonized, and then the coke producedis pushed out of the ovens, all according to a predetermined time cycleor sequence and only at the time that the coke is being pushed out ofthe ovens are the connections of the oven with the gas mains cut o.

It is very desirable to maintain a substantially' uniform temperaturethroughout the whole depth of the coal bed in each horizontal coke ovenin a battery during carbonization of the coal, and various expedientshave been tried with little success to achieve this desideratum. As thebattery of ovens operates on a time sequence, some ovens will be gassingfreely While others in which carbonization is more nearly complete willhave more or less stopped gassing. Under the latter condition, there isgreat danger that the temperature of the oven charge will rise withconsequent over-heating of the gas space. Such overheating causescracking of the hydrocarbon vapours and ammonia which are formed by the.coal carbonization, and thus tends to crack all or part of theby-products and to decrease the value ofv the by-products obtained. Sucha cracking operation also acts to form carbon which builds up on thewalls of the oven and which interferes with the heat transference fromthe heating ues to the oven chamber and the proper carbonization of thecoal.

It is proposed in the specification of the copending United Statespatent application No. 627,378 of Koppers Company Inc., now Patent -No.2,541,794, to control the temperature of the gas and vapour in the spaceat the top of each oven, while permitting the maintenance of the desiredtemperature in the coke bed, by effecting a positive circulation ofcooled gases through the gas space at the top of the oven in alternatingdirections so as to maintain a substantially uniform temperature in thegas space. The circulated gases are those contained in the gas spaces ofthe ovens, the collecting mains and the gas otake mains or archedcross-duct of the battery or group of ovens. about 40 feet long itfollows that cooled gases passed into one end of an oven gas space froma gas collecting main increasein temperature as they pass through thegas space so that when the gases reach the opposite end of this gasspace their temperature is nearly that of the coke bed. It is for thisreason that gases in the said circuit comprising the gas collectingmains, gas oitake mains or cross-duct and the gas spaces of the ovensare alternately circulated in opposite directions, this change ofdirection being effected at frequent intervalsv so as to bring thecooled gases alternately into the opposite ends of the oven gas spacesin suflicient quantities to maintain a substantially uniform temperaturethroughout the lengths of these spaces, this temperature being lowerthan that at which the hydrocarbons and ammonia products will bedecomposed.

The alternate circulation of the cooled gases in opposite directions iseffected, according to the said Koppers patent application No. 627,378,by means of a pair of independent fans arranged one in each verticalpart of the arched oitake main or cross-duct and adapted to circulatethe gases therein in opposite directions, automatic timing and switchmeans being provided so as to bring the two fans alternatelyintooperation so that first one fan circulates the gases through theoven gas spaces in one direction and then the other fan circulates thesegases in the opposite direction whilst the rst fan is at rest,` afterwhich the rst fan comes into operation again and the second fan rests,and so on throughout the operation of the battery or groups of ovens,`it being generally found desirable to effect this reversal of the gasflow direction at about five minute intervals although the duration ofthese intervals may be varied widely, say between two and sixty minutes,depending for example upon the type of coal being carbonized, the typeof coke being made, and the type of gas being produced, it beingdesirable however to maintain the temperature in the said gas spacessuiilciently low to prevent the decomposition of the by-products beingmade, as previously explained.

An object of this invention is to provide an im- As the ovenslareusually.

proved means of eiecting an improvement in the said alternatecirculation of cooled gases through the gas spaces of the ovens inopposite directions and according to this invention there is provided,in a cokev oven battery, a gas duct which is in communication atopposite ends with the gas collecting mains at the opposite sides of thebattery, and a rotary fan or impeller (hereinafter referred to as a fan)which is located in said gas duct for circulating the gasesin the gasspaces of the ovens and the said gas collecting mains alternately inopposite directions, such fan being adjustable as to the position of itsfan blades in its gas duct so as to be capable itself of causing thesaid alternating ow of gases by the change in position of the fariblades without change in its own direction of rotation-i. e. withoutreversing its motor'.

The said gas duct containing the said fan may be the arched offtake mainor cross-duct of the battery but preferably it 'is an additionalseparate gas-duct arranged in parallel with and bridging the said archedoitake main or cross-duct.

According to a further aspect of the invention, there is provided incombination, a battery of horizontal coke ovens arranged side by side,gas collecting mains communicating with the opposite ends of the saidovens at the upper parts thereof, offtake mains extending from each ofthe said collecting mains to a connecting T, a suction main for leadingthe gas away from said T, an adjustable rotary fan in a gas duct fordrawing gases from one of said collecting mains through said oiitakemains and forcing these gases back into the other collecting main andthrough the gas spaces of the said ovens in one direction and for thendrawing gases from the second of the said collecting mains and throughthe gas spaces of the ovens in the opposite direction to the previousflow, and means for adjusting said rotary fan to alter the position ofits blades in its gas duct for causing it alternately to eiiect the saidopposite iiow of gases.

According to a further feature of the invention the blades of the saidian are arranged so that their pitches or angles of attack may beadjusted through a range of positive positions, a neutral position and arange ox' negative positions whereby the lan may be adjusted to give aflow of gases in either direction through the said gas duct or so as toproduce a static or -no now condition, and whereby the quantitativevalue of the gas How in either direction can be regulated.

The ian is preferably driven by a uni-directional continuously operatingconstant-speed electric motor developing suiicient power for the maximumgas ow required, the actual gas flow being varied as desired byadustment of the pitch of the blades of the fan and not by adjustment Yof the running speed oi' the motor.

Variation of the pitch of theblades of the fan may be provided for bymounting each blade for rotational adjustment about its own axisrelatively to the fan shaft.

Thus, according to a further aspect of the invention, there is providedin combination a battery of horizontal coke ovens arranged side by side,gas collecting mains communicating with the opposite ends of the gasspaces of the said ovens at the upper parts thereof, an oitake mainleading from each of said collecting mains, a suction main connected toboth of said oiltake mains at the ends thereof remote from the saidcollecting mains, a gas duct bridging the said olftake mains. gascirculating means in said bridging gas duct for circulating gases insaid collecting mains and ofl'take mains alternately in oppositedirections through the gas spaces of the said ovens, such circulatingmeans comprising a fan in the bridging gas duct having its bladesrotatable in its hub to vary and reverse their pitch respectively foreffecting a variation in the quantitative flow of said gases thereby,and also to reverse the direction of flow of the gases thereby throughthe bridging gas duct, means for effecting the variation and reversal ofthe pitch of said fan blades, and a constant-speed electric motor fordriving said fan to run in one direction only.

The rotational adjustment of the blades of the fan may be controlled byany suitable hydraulic, pneumatic, electrical or mechanical means or acombination of such means which itself may be controlled manually orautomatically. For example, suitable timing gear may be embodied in theapparatus automatically to control the pitch varying and reversingmechanism of the blades of the fan to eect changes in the quantitativeow of the gas and also the change of direction of the gas flow and, ifdesired, to provide a Yariable delay or pause between the change-overfrom gas now in one direction to gas flow,in the opposite direction. Forinstance, to eiect the said ldelay or pause the said timing gear mayprovideu for retaining the fan blades, during the reversal of the pitchof the blades, in /a neutral position for a predetermined period )whilstthe fan motor continues to run at its synchronous speed, the fan bladesthereafter cntinuing to move to the position for reversing the gas iiow.

In an alternative arrangement, the rotary fan may be of the fixed bladeuni-,'irectionai type and be mounted in the gas du t for bodilyadjustment of the ian blades and their drive shaft through relatively tothe duct in order to reverse its direction of thrust, such reversal ofthe fan as a unitary whole being ellected through any suitabiehydraulic, pneumatic, electrical or mechanical means (or a combinationof such means) which may be remotely controlled or controlled throughautomatic timing mechanism in a manner similar to that above referredto.

In such an arrangement, means may also be providedfor varying the speedof the motor in order quantitatively to ycontrol the gas flow throughthe gas duct.

According to a still further aspect of the invention, there is providedin combination a battery of horizontal coke ovens arranged side by side,gas collecting mains communicating with the opposite ends of the gasspaces of the said ovens at the upper parts thereof, an ontake mainleading from each of said collecting mains, a suction main connected toboth of said oltake mains at the ends thereof remote from the saidcollecting mains, a gas duct bridging the said offtake mains. means insaid bridging gas duct for circuiating gases alternately in oppositedirections in said collecting mains and offtake mains and through thegas spaces of the said ovens, said means comprising a rotary fanadjustable as a unitary whole through 180 in said bridging duct toreverse its direction of thrust, means for driving said fan, and meansfor effecting the adjustment of the'said fan as a unitary whole through180.

According to a still further feature of the invention. when the fan orfans is or are arranged in a gas duct which is additional to-i. e. whichis in parallel with or bridges-the offtake main or cross-duct, a valveor damper may be provided in the oiIta-ke main or cross-duct at thejunction of the suction main therewith so as to prevent circulation ofthe gases in this otake main or cross-duct, such valve or damper beingadapted automatically to reverse its position to place opposite sides ofthe offtake duct into communication with the suction main each time thesaid fan in the additional gas duct is operated to reverse the ow of thecirculating gases.

It will thus Ibe apparent that this invention provides for the use of asingle fan itself adapted to provide alternate flow of the gases in eachof the two opposite senses orfdirections, thus rendering unnecessary aseparate fan for driving the gases in each of the said two directions,and eliminating the braking action such fans tend to impose, when idle,on the gas flowing out through the collecting and exhaust mains.However, although only a single fan of the aforementioned character willnormally be used for each of said gas ducts it should nevertheless beunderstood that if desired two or more such fans may be used, these fansbeing arranged to operate, and be adjusted, in tandem or unison so as toassist one another.

In order that the nature of the invention and the method of carrying thesame into effect may be more readily understood two embodiments of thesame will now be described by way of example with reference to theaccompanying drawings, in which:

Figure 1 is a fragmentary view, partly in elevation and partly incross-section, showing diagrammatically the upper part of a coke ovenbattery with its gas collecting mains, oitake mains and the suction-main therefor;

Figure 2 is an enlarged diagrammatical vertical part-sectional view ofthe gas collecting fan shown in Figure 1;

Figure 3 is an enlarged vertical sectional elevation diagrammaticallyshowing the blade controlling mechanism of the fan shown in Figure 2;

Figure 4 shows a modication of Figure 1;

Figure 5 diagrammatically illustrates a modied form of fan unit for usein an arrangement such as is shown in Figure 1; and

Figure 6 is a plan of the unit shown-in Figure 5.

In the accompanying drawings, the present invention is shown as appliedto a Becker-type coke oven of the kind described in the specification ofUnited States Patent No. 1,752,363.

The coke oven battery is of the horizontal character where wherein aseries of ovens, such as the oven\l of which the upper part is shown inFigure 1, are arranged side by side with heating nues (not shown) onopposite sides of each oven. The ovens of such a battery are usuallyoperated as a unit, each of the ovens being connected with gascollecting mains 2 and 3 arranged horizontally one on either side of thebattery adjacent the crown 4 thereof and disposed with their lengthsperpendicular to the lengths of the ovens I.

The ovens are provided at the oppoiste ends respectively with removablesealing doors 5 and 6.

Each oven I is charged with coal through charging openings I in thecrown 4 of the oven after which these openings are sealed. The top oithe coal bed 8, in each case, is levelled by a leveller bar which isinserted through an opening 9 in the door 6 of the oven. A space I0 isthus left between the crown 4 of the battery and the top of the coal bed8 in each oven and this space is herein referred to as the gas spaceI0."

The heating nues which are located between the ovens are continuouslyheated while the battery is in operation and as gases are formed in eachoven by the carbonization process these gases rise from the oppositeends of the gas space I0 of the oven and pass upwardly through ascensionpipes Il and l2 arranged one adjacent each end of the battery andrespectively connected, by intermediate ductings I3 and I4, to the gascollecting mains 2 and 3.

Preferably arrangements are provided whereby, as the gases pass to thegas collecting mains 2 and 3, they are met by sprays of ammonia liquorintroduced through appropriate spray pipes (not shown)-which act to coolthe gases to a temperature in the region of C. At this stage thegenerated gases may also be saturated with water vapour to increasetheir thermal capacity.

The collecting mains 2 and 3 have the lower ends of vertical portions I5and I6 of an arched offtake main or cross-duct 2| respectively connectedthereto, and these vertical parts of the oitake main continue inwardlyrespectively in horizontal portions II and I8 extending transverselyacross the top of the battery to a T-joint I9 to which is connected asuction main 20. The arched offtake main 2I is bridged by a gas duct 22arranged in parallel with the portions I'I and I8 of the oiftake mainand connected at its opposite ends respectively to the vertical parts I5and I6 of this oitake main.

The oitake main or cross-duct 2| is conveniently located approximatelycentrally between the ends of the battery. but it can be arranged in anyother suitable position with respect to the battery, for example at oneend thereof; moreover, Where desired two or more of these ofltake mains2| may be employed at positions spaced along the length of the battery,such oitake mains being connected to separate or to a common suctionmain.

In order to maintain a more or less uniform temperature in the gasspaces I0 of the ovens whilst retaining the temperature in these spacesbelow that at which the hydrocarbons and ammonia by-products would bedecomposed, cooled gas is circulated through the gas spaces IIJalternately in opposite directions, and to effect this alternatingcirculation a rotary fan 23 is located within, and preferably centrallybetween the ends of, the gas duct 22.

The fan 23 has a plurality of blades-e. g. two, three or more-soarranged that their pitches or angles of attack may be adjusted througha range of positive positions, a neutral position and a range ofnegative positions whereby the fan may be adjusted to give a ow of gasesin either direction through the gas duct 22 or to feather and so producea. static or no-ow condition and whereby the quantitative value of thegas flow in either direction can be regulated, this being effected byadjusting the pitches or angles of attack of the blades suitably betweenthe maximum positive or negative positions and their neutral positions.

In the examples shown in the accompanying drawings, which as alreadystated are of a. diagrammatic character, the fan 23 has twodiagrammatically opposite similar blades 24 and 25, the roots 26 and 21of which are rotatably mounted in a cage or hub 28 fixed upon afan-driving hollow shaft 29. Although the roots 26 and 21 of the blades24 and 25 are rotatable in the cage 28 they are restrained by anyappropriate means against axial movement in this cage.

The shaft 29 is rotatably supported in horizontally spaced bearings 30and 3| carried by a skeleton supporting structure 32 depending from ahousing 34 carried by a vertical trunking 34 built onto the upper sideof the cross-duct 22 so that the fan shaft 29 is located coaxially inthe gas duct 22.

A constant-speed electric motor 35 is mounted Within the housing 34 anddrives the fan shaft 29 through pulleys 36 and 31 and a belt 33 whichmay be a plain belt or of a multiplesection type as desired.' suitablemeans (not shown) being provided for appropriately tensioning the beltor belts.

A fan blade pitch-adjusting or feathering shaft 39 is co-axially mountedin the hollow fan-shaft 29 for axial adjustment on the latter and thisfeatheringlshaft projects beyond both ends of the fan shaft..` -The fanend of the feathering shaft 39 carries'a fan-blade feathering head 40furnished with a pair of racks, 4| and 42 (see Figure 3), arrangedopposite each other diametrically of the shaft 29 and parallel to thelatter, each of these racks being guided in the cage 28 and meshing witha corresponding toothed wheel fixed coaxially upon the root of thecorresponding fan blade 24 or 25, rack 4| meshing with the toothed wheel43 on the blade 24 being marked in the drawings with a reference 43 andrack 42 meshing with toothed wheel 44 on the blade 25.

The racks 4| and 42 are so arranged with respect to the wheels 43 and 44that as the feathering shaft 39 is moved axially in one direction in thedriving shaft 29, the blades 24 and 25 turn simultaneously andcorrespondingly in one direction, and as the shaft 39 is moved inopposite directions like rotation of the blades occurs but in a reversedirection so that by appropriately axially adjusting the featheringshaft 39, the blades 24 and 25 can be moved from a maximum positive flowposition gradually to a fully feathering or neutral position and thenfurther onwards through gradually increasing negative positions to amaximum flow negative position. Thus. by this means gas can be caused toflow in the gas duct 22 in the direction of the arrows shown in Figure 1and can subsequently be caused, by reversing the pitches of the bladesof the fan, to flow in an exactly opposite direction from that indicatedby the arrows. Alternatively the blades can be set in their neutralposition sdthat there is a static or no-iiow condition in the duct 22.In addition, by axially adjusting the feathering shaft 39 appropriately,any quantitative value of the gas ow between zero and the maximumcapacity of the fan can be achieved in either of the said twodirections.

The axial adjustment of the feathering shaft 39 may be effected througha grooved collar 45 xed on the end of the feathering shaft 39 oppositeto that end carrying the fan 23, the axial adjustment of the collar 45being controlled by a pivoted lever 46. This level itself is controlledby any suitable means, for example a hydraulically or pneumaticallyoperated piston, an electric motor and screw or by rods and levers, orthe lever 46 may be operated through automatic time-controlled mechanismwhich may include an electric motor (which can be the fan motor 35)furnished with one or more cams for controlling the action of the lever46.

The arrangement should preferably be such that the duration of the iiowof gases in either direction along the gas duct 22 can be varied asrequired. and should also provide for the'variation in the quantitativenow of gases from the `duct in either direction as well as for thevariation in the period during which the blades of the ian remain intheir no-Iiow or neutral position. it being desirable, in some cases, tohave me blaues pause in this position for a period and it is desirablethat this period should be variable to suit any particular set ofcircumstances.

The mechanism for actuating the lever 46 for controlling tne operationor the pitch of the fan blades is not illustrated in the drawings as itwill be clear that a variety of weil-known sequence-controllingmechanisms can be adapted for the present purpose.

The fan motor 36 is preferably a constant-speed motor which will runcontinuously whilst the battery of ovens is operating, variation in thequantity of gas ow along the duct 22 being achieved by modification ofthe settings of the blades 24 and 25 of the fan 23 rather than byvariation in the speed of the motor.

To cool the motor 35 and the fan shaft bearings 30 and 3|, the housing34 is conveniently provided with louvres 4| to admit a certain quantityof air to the housing whilst, if desired, one or more fresh air inlets46 may be adoitionally provided to admit outside air (which can be underpressure from a secondary fresh air fan-not shown) into the housing 34for similar cooling purposes, but this cooling air is not conveyed intothe gas duct 22 since the skeleton framew'rk 32, the fan shaft 29 andits bearings 30 and 3|, the belt 36 and the mechanism 46 are enclosed bya casing 49. In addition, to the head of the fan 23 is furnished with aspinner 50 and the casing 49 protrudes through a semi-circular flaring22' which forms a continuation or junction for the gas duct 22 where thecasing 49 and the associated parts penetrate into this gas duct.

In the oli'take main or cross-duct 2|, at the T-joint I9, a valve ordamper 5| is provided which is adjustable to segregate either the partI6 of the ofitake main or the part I1 of the latter from the suctionmain 20, and this valve 5| is preferably so coupled with the lever 46 orany other suitable part of the fan blade controlling mechanism that thevalve 5| reverses its position each time the lever 46 reverses thedirection of flow of gases through the duct 22, thereby ensuring thatthe upper part of the oitake main 2| is excluded from the recirculatingsystem comprising the gas duct 22, the vertical gas offtake main partsl5 and I6, the gas collecting mains 2 and 3, the ascension pipes and |2and the gas spaces I9 of the ovens. 'f

It will thus be seen that gas is alternately circulated through the gasspaces I0 of the oven from opposite ends, first in one direction andthen in the other direction, the rate of change of the direction ofcirculation and also the quantity of gas circulated being adjusted toprovide for the maintenance of the temperature in the gas spaces belowthat which will be harmful to the by-products which it is desired toproduce by the carbonization process.

A modification of the arrangement above described is shown in Figure 4of the drawings where two of the fan units shown in Figure l are used inthe gas duct 22, these units being marked respectively 34 and 34"in'Figure 4. Otherwise the arrangement is precisely the same as thatdescribed with respect to Figures 1 to 3. Where two or more fans areused in the duct 9 22 in this way, these fans are arranged to work intandem or unison so as to operate together and assist one another.

Figures and 6 show a further modification according to this inventionwherein, instead of using a variable pitch fan driven by a constantspeedmotor, the fan 52 is of the fixed-blade variety but its housing 34a ismounted for rotation by any suitable means, such as meshing bevel gears53 and 54, through 180 in the duct 22 so that the fan can beA arrangedto propel gas through the duct 22 in either direction therealong-i. e.reversing the position of the fan blades in the duct 22, withoutchanging the direction of rotation of the fan. In this case, variationin the rate of iiow of gas through the duct can be modified to someextent by the rotation of the housing 34 about its vertical axis, butadditional variation can be achieved by varyingr the speed of the motordriving the fan. A substantially no-flow condition would arise when themotor had been turned through 90 from the position shown in Figure 1 buta complete stoppage of ilow of the gases through the duct 22 can beachieved by stopping the rotation of the fan altogether.

From the foregoing description, it will be appreciated that apparatusaccording to this invention enables a proportion of the generated gases(which has not been removed through the suction main but which has beenpartially cooled by passage through the gas collecting mains) to berecirculated through the gas spaces at the tops of the ovens. When thefan 23 in the gas duct 22 is in the no-flow condition the generatedgases do not ow through the gas duct 22; but gas may pass off from bothmains 2, 3, in such case, if desired, through the oiitake main 2l directto the suction main 20, the valve 5I being held in a mid-position atthis time.

It will be further understood that the apparatus according to thisinvention comprises a simplication of that described in the saidco-pending United States patent application No. 627,378 of KoppersCompany Inc. for carrying out the method of recirculation described andclaimed in that patent application.

What I claim is:

1. The combination with a battery of horizontal coke ovens arranged sideby side, gas collecting mains communicating with the opposite ends ofsaid ovens at their crown spaces in the upper parts thereof, an oitakemain leading from each of said collecting mains, and a suction mainconnected to both of said oiitake mains at a position remote from saidcollecting mains: of a gas duct bridging said offtake mains andby-passing the suction main. means in said bridging gas duct forcirculating gases in said collecting mains, through their offtake mains,alternately from one to the other,

' and thence through the gas crown spaces of said ovens alternately inopposite directions, said circulating means comprising a fan havingblades rotatable about their axes to vary and reverse their pitch,respectively, for effecting a variation in the quantitative iiow of saidgases, and to reverse the direction oi' ow of the gases, respectively,means for effecting the variation and reversal of the pitch of theblades of said fan, and a constant-speed electric motor for driving saidfan.

2. Apparatus as claimed in claim l, and which includes an adjustablevalve controlling the flow of gases alternately from said otake mains to10 said suction main, and means to operate said valve to alternate theconnection of said two ofitake mains to said suction main in step withthe reversal of the pitch of the blades of said fan, for reversal forflow of gases through the said bridging duct.

3. The combination with a battery of horizontal coke ovens arranged sideby side, gas collecting mains communicating with the opposite ends ofsaid ovens at their crown spaces in the upper parts thereof, an offtakemain leading from each of .said collecting mains, and a suction mainconnected to both of said oii'take mains at a. position remote from saidcollecting mains; of a gas duct bridging said offtake mains andbypassing the section main, means in said bridging gas duct forcirculating gases in said collecting mains, through their offtake mains,alternately from one to the other. and thence through the gas crownspaces of the said ovens alternately in opposite directions, said meanscomprising a rotary fan adjustable through 180 in said bridging duct toreverse its direction oi' thrust, means for driving said fan, and meansfor effecting the adjustment of the said fan through 180.

4. The combination with a battery of horizontal coke ovens arranged sideby side with heating fiues therebetween, gas collecting mainscommunicating with opposite ends oi the gas crown spaces at the upperparts of said ovens, an oiitake main leading from each of saidcollecting mains, and a suction main connected to both of the saidofltake mains at a position remote from said collecting mains; of a gasduct bridging the said offtake mains and by-passing the suction main,and fan means in said bridging duct, said fan means comprising anadjustable fan and means to cause said fan to circulate gases cooled insaid collecting mains alternately in opposite directions through thebridging duct, from one to the other of the oiitake means, and thence totheirgcollecting mains and through the gas crown spaces of the owens forreverse iiow in alternation therethrough.

5. The combination with a battery of horizontal coke ovens arranged sideby side, gas collecting mains communicating with the opposite ends ofsaid ovens at their crown spaces in the upper parts thereof, an oiitakemain leading from each of said collecting mains, and a suction mainconnected to both of said oiitake mains at a position remote from saidcollecting mains; of a gas duct bridging the said offtake mains andby-passing the suction main, means in said bridging gas duct forcirculating gases in said collecting mains, through their oiitake mains,alternately from one to the other, and thence through the gas crownspaces of said ovens alternately in opposite directions, saidcirculating means comprising a multi-bladed fan having a hub and theroots of the blades rotatably mounted in the hub, a hollow fan shaft onwhich the hub of the said fan is fixed, an electric motor for drivingsaid fan shaft, a support for suspending the said fan shaft and the fanaxially in said bridging gas duct between the ends thereof, gear wheelsiixed on the roots of said fan blades, a reciprocable rack for andmeshing with each of said gear wheels, a fan blade pitchadjusting shafthoused in said hollow fan shaft for axial sliding movement relativethereto and having said racks attached thereto at the fan end thereof,and means for axially adjusting said pitch adjusting shaft to varycorrespondingly the pitches of all the fan blades simultaneously, for

eecting quantitative variation and reversal in 1 1 direction of gas owthrough said bridging duct by said gas circulating means.

6. Apparatus as claimed in claim 5, and in which said fan shaft islocated coaxially within said bridging gas duct and said electric motorfor driving the fan is disposed outside the outer confines of said duct,al1 the parts except the fan blades being housed unitarily in a. housinglet into the upper part oi' the said gas duct and closed to the interiorthereof.

CYRIL REFERENCES CITED The following references arev ot record in thetile of this patent:

12 UNTTED STATES PATETS Number Number Name Date Yingling July 6, 1948Koppers Feb. 22, 1921 Becker Apr. 1, 1930 Connors Sept. 30, 1930 MadderOct. 1, 1940 FOREIGN PATENTS Country Date Germany Dec. 23, 1940 GermanyFeb. 27, 1932 Great Britain Jan. 12, 1933

